Poorly Cherry Tree

My ornamental cherry tree (in my profile pic) is poorly and has been for a couple of years and I think I may know what is wrong but I'm not sure, and I'm not sure how to treat it.

A you can see, it comes into blossom beautifully! But the blossoms literally only last a week before they all die. They turn brown and are left just hanging from the branches. Also the leaves don't grow, especially on the lower branches.

I tried to upload a pic but it won't let me.

Anyway, I think it is Blossom Blight/Brown Rot.

It says to cut off all infected branches and use a fungicide.

My questions are;

Is it blossom Blight?

If I have to cut off all the braches, will the tree spur new ones or will it be beyond saving?

Where do I get fungicide from?

I am a very new gardener and a bit out if my depth with this one, so any help is much appreciated

Many thanks

Carrie